The companion modeling framework brings together experts (biophysical and social scientists) and local and global knowledge, perceptions and concerns over natural resources by the way of participative modeling supports (role playing games and agent based computerized modeling) that are used during multi-stakeholder platforms (MSP) in two watersheds in Ghana and Burkina Faso. The companion modeling process is used together with a biophysical model (see corresponding abstract VSSe007) to get a "sound" scientific representation of the impacts that local practices can have in space and time. It allows considering multiple points of views (e.g. multi-level and multi stakeholders) about issues, potential solutions and their impacts. A better understanding of possible solutions and their impacts is the first step towards a process of collective decision making to design acceptable water resources practices. Multi-level MSPs allow for actors (from local stakeholders to national policy makers) that do not interact often to confront, be aware and understand each other's views better. The novelty of the project is that the focus is on reinforcing the process of collective decision making rather than on reaching an agreement on a specific issue. This fits well with the multi-faceted nature of IWRM. The approach requires constant stakeholder engagement and trust building at multiple levels and is facilitated by earlier knowledge of the actors and systems studied. (Texte intégral)